The present invention relates to the technical field concerning the sterilisation of apparatuses or bottles for pharmaceutical use.
More particularly, the present invention relates to a method for sterilising the inside of a bottles sterilisation oven, and to an oven which carries out said method.
It is known that all the different kinds of bottles for pharmaceutical use, which are made of glass or the like, must be submitted to a sterilisation process before filling them with a drug, in order to destroy or inactivate all the microorganisms that potentially could adulterate the bottles content, or that could be harmful for a patient to which said drug has to be given.
The bottles sterilisation is usually carried out at high temperatures, inside a special sterilisation oven, which is configured as a xe2x80x9ctunnelxe2x80x9d, and which is stepless operated, for productivity purposes.
The known sterilisation tunnel-type ovens normally comprise three cascade-connected and intercommunicating sections: an input chamber, a sterilisation chamber, also called hot chamber, and a cooling chamber for the sterilised bottles. The three above sections are crossed by a tape conveyor, that forwards the aforesaid bottles in sequence through all the sections.
The input chamber has an input door, through which the bottles, coming from a washing station, are fed to the oven. At the opposite end, the cooling chamber is provided with an output door for communicating with a sterile room, wherein bottles are filled with a drug and then sealed.
The hot chamber is provided with suitable heaters, operable to heat the said chamber to a given temperature, which is high enough to sterilise all the bottles continuously passing therein.
Bottles stay in the cooling chamber until their temperature attains a value approaching that of the subsequent sterile room. Said chamber is suitably provided with working fluid type heat exchangers, which help in lowering the air temperature inside the chamber, and consequently in lowering the bottles temperature.
All the sterilisation oven sections are normally submitted to a laminar flow of air filtered by H.E.P.A. filters of suitable retention characteristic features. They are kept in a slight plenum condition, in order to avoid any non-filtered air, which is therefore contaminated by particles and microorganisms, to flow into the oven.
But, in the conventional sterilisation ovens, neither the input chamber nor the cooling chamber are intrinsically sterile. In fact, although they are subject to a continuous laminar flow of filtered air, their inner surfaces could contain some contaminating agent, that could pollute the bottles. This is a serious drawback, particularly for the cooling chamber, which contains already sterilised bottles of course, the hot chamber is intrinsically sterile.
The aforesaid possibility of bottles contamination, although it is normally very poor, is taken in particular account by all the pharmaceutical companies and surveillance organisations, and a great number of requests for ovens provided with a sterile cooling chamber is arising.
Some ovens provided with periodical sterilisation procedures for the cooling chamber are known, particularly by heating it to a temperature similar to those reached in the hot chamber, in order to kill all the pathogenic agents. This solution is extremely expensive and difficult to carry out and to sell. In fact, because of the cooling chamber size, high power heating assemblies must be provided; all the power lines and apparatuses that carry the power to the oven must be sized accordingly, and then practically doubled with respect to a conventional sterilisation oven.
It is an object of the present invention to propose a method for the periodical sterilisation of the cooling chamber, and of the whole sterilisation oven, which can be carried out without heating the same oven.
A further object of the present invention is to propose a such method which doesn""t significantly improve the oven production costs nor its power consumption.
A further object is to propose a sterilisation oven which is totally cold sterilisable, accordingly to the aforesaid method.
The aforesaid objects are achieved by a method comprising the steps of:
air tightly closing oven input and output openings and input and output ducts;
opening forced input means, for introducing a mixture of air and of sterilisation fluid into the oven;
supplying a pre-defined amount of a mixture of sterilisation fluid and air, until a pre-defined static pressure is attained;
opening at least one output duct for the sterilisation fluid;
stopping the supply of the sterilisation fluid, and supplying the oven with humidity controlled air, until the percentage of said sterilisation fluid inside the oven falls down to a pre-defined value;
closing said forced input means and said output duct, and re-opening the input and output opening.